This invention concerns glycol-based aircraft anti-icing fluids which are thickened with carrageenan, a sulfated polysaccharide gum derived from marine algae.
Aircraft that are either parked on the ground or are on the ground between flights can accumulate snow, ice or frost on the aircraft surfaces in cold winter weather. The presence of such deposits, particularly on airfoil surfaces, is highly undesirable during takeoff and flight since even small accumulations can result in severe deterioration of the airfoil aero-dynamic performance characteristics.
Ethylene glycol has long been used in aqueous solutions of various strengths that are sprayed onto the aircraft, as a deicing agent, to remove snow, ice and frost deposits from aircraft surfaces. After this treatment, the glycol fluid desirably remains as a film coating on the aircraft surfaces, to serve as an anti-icing agent that provides continued antifreeze protection and minimizes the further formation or accretion of snow, ice or frost deposits on the aircraft surfaces. The same glycol-based fluid, in various concentrations, may be used for both deicing and anti-icing functions.
Glycol-based fluids for anti-icing, however, typically contain a thickening agent and desirably possess the following attributes (none of which preclude its use as a deicer):
formation of an essentially continuous film coating, after its application by conventional spraying devices, even on non-horizontal aircraft surfaces PA1 extended, long-term protective anti-icing action PA1 viscosity and rheology characteristics that promote formation of an effective tenacious protective film coating, yet enable the fluid coating to flow off the aircraft airfoil surfaces during takeoff, prior to aircraft rotation. PA1 (a) glycols (40-60%), preferably ethylene glycol, propylene glycol and/or diethylene glycol; PA1 (b) water (35-60%), with glycol and water being at least 94% of formulation; PA1 (c) cross-linked polyacrylate thickener (0.05-1.5%), having a specific viscosity and special flow properties; PA1 (d) mixed-based mineral oil (0.05-1%); PA1 (e) alkylaryl-sulfonate surfactant (0.05-1%); PA1 (f) corrosion inhibitor (0.01-1%); and PA1 (g) an alkaline compound like KOH to adjust the pH to 7.5-10.
U.S. Pat. No. 4,358,389 issued to Konig-Lumer et al. describes a multicomponent glycol-based deicing/anti-icing fluid for treating aircraft, and its formulation is believed to be representative of glycol-based deicing/anti-icing agents in commercial use:
The patent indicates that other additives, such as anti-oxidants or additional thickeners, can also be present. Polysaccharide gums like xanthan may be used as additional thickeners, since they improve the performance characteristics of the specified polyacrylate thickeners.
The present invention is based on the unexpected discovery that gel-forming carrageenan gum possesses particular efficacy as a thickener for glycol-based aircraft anti-icing fluids.